Use http2 directive instead of listen ... http2

[chubei]

Is your feature request related to a problem? Please describe.

nginx-ingress currently doesn't support enabling HTTP2 unless using TLS.

Describe the solution you'd like

In nginx 1.25.1, HTTP/1.1 and HTTP/2 on same TCP stream is supported, with the new http2 directive. We can use it in the latest nginx-ingress.

Describe alternatives you've considered

None.

Additional context

None.

[brianehlert]

There are a number of changes that are happening around the http2 directives, if you have not noticed.
Right now we are evaluating how to align with http2 directive deprecation as well as new directives and patterns.
I think this is just one part of that larger amount of effort.

[brianehlert]

Added work item here: #4237